Effects Of Castanopsis Eyrei On Soil Organic Carbon Components

Fallen wood is an important part of forest ecosystem.It has important ecological significance in forest regeneration,species diversity,water conservation,prevention of soil and water loss,nutrient supply and carbon cycle.At present,the research on fallen wood mostly focuses on the storage and the variety of nutrient elements in the process of fallen wood decomposition,and there are relatively few studies on the change process of soil organic carbon composition and bacterial community structure.To explore the effect of falling wood on soil organic carbon fractions,soil physicochemical properties and soil bacterial community structure,and provide a scientific basis for the effect of falling wood on soil carbon pools.Here,the method of space substitute time was used to select fallen wood in two natural Castanopsis eyrei forests at different altitudes,and according to the previous classification of fallen wood and combined with the actual situation,the fallen wood in the sample plot were divided into three decay grades:light decay(Ⅰ),moderate decay(Ⅱ)and severe decay(Ⅲ).We collected soils at 0-15,15-30 and 30-45 cm under fallen wood,and the same depth soil was collected in areas without falling wood as controls(CK).The main research findings are as follows:1.There was no significant difference in soil moisture content with or without fallen wood cover,but the soil moisture content under the fallen wood with severe decay was higher than that under the fallen wood with mild decay,and the soil moisture content under the fallen wood with severe decay was 14.46%higher than that of the control.The soil pH under the fallen wood was lower than that of the control,and there was no consistent change law of pH with the decay grade.The soil organic carbon and total nitrogen of fallen wood mulching were significantly higher than those of the control group(P<0.05),and showed an upward trend with the increase of decay grade,soil organic carbon and total nitrogen in high altitude areas were significantly higher than those in low altitude areas.Soil C:N<20:1,indicating that the growth of soil microorganisms may be limited by carbon.2.Fallen wood has an important impact on soil stability.In the 0-15 cm layer,the mean weight diameter of soil aggregate(MWD)and the geometric mean diameter of soil aggregate(GMD)were significantly higher than that of the control;With the increase of soil layer,the mean weight diameter and geometric mean diameter show a decreasing trend;It shows that the stability of topsoil in contact with fallen wood has been improved.The mean weight diameter and geometric mean diameter in high altitude areas were significantly lower than those in low altitude areas(P<0.05).Organic carbon and total nitrogen are mainly distributed in aggregates with particle size of 0.053-0.25 mm.With the increase of particle size of aggregates,the contents of organic carbon and total nitrogen show a decreasing trend.With the increase of soil layer,the carbon and nitrogen content of soil aggregates with each particle size decreased.3.In high altitude areas,soil amylase,sucrase and urease showed a significant increasing trend with the increase of decay grade(P<0.05),and the activities of these three kinds of soil enzymes under fallen wood were significantly higher than those in the control group without fallen wood.The catalase activity under the fallen wood in 0-15cm soil layer was significantly higher than that in the control(P<0.05).In the low altitude area,only in the 0-15cm soil layer,the activities of sucrase and amylase in the soil below the heavily decayed fallen wood were significantly higher than those in the control(P<0.05),and the activities of urease and catalase were not consistent with the decayed fallen wood.4.The relative abundance of soil bacteria under fallen wood was higher than that of the control.Through the redundancy analysis of environmental factors and soil microbial community,it is found that soil organic carbon and pH are the key factors driving microbial community.The distribution of soil bacterial community under light decay fallen wood is similar to CK,which is significantly different from that under moderate and severe decay fallen wood.The abundance of soil bacterial community and soil active organic carbon components are most affected by heavy decay fallen wood.5.The active organic carbon changed significantly after being covered with fallen wood.The soil easily oxidized organic carbon,light and recombined organic carbon and microbial biomass carbon were significantly higher than the control(P<0.05).The content of soluble organic carbon increases with the increase of decay,but the content of soluble organic carbon under the fallen wood is lower than that of the control.Active organic carbon decreased with the increase of soil layer.Different altitudes have significant effects on the organic carbon fraction.The active organic carbon in high altitude areas is higher than that in low altitude areas.Pearson correlation analysis showed that organic carbon components were mainly positively correlated with Actinomycetes,soil enzyme activity,organic carbon,total nitrogen and water content,and negatively correlated with pH.To sum up,significantly different in soil organic carbon fraction in fallen wood mulching compared with CK,and the decomposition of fallen wood had an increasing effect on soil organic carbon fraction.Total nitrogen is the key factor affecting organic carbon fractions,organic carbon fraction is positively correlated with soil enzyme activity and Actinomycetes are the main bacterial community affecting organic carbon content.This research will help to clarify the impact of fallen wood on soil organic carbon fractions,to in-depth understand the interaction between organic carbon fractions,soil enzyme activities,and soil bacterial communities.Furthermore,to improve the function of fallen wood in the carbon cycle of forest ecosystems and provide a scientific theoretical basis for the biogeochemical cycle of fallen wood in forest ecosystems.